1. Field of the Invention
The present invention relates to a structure and a fabrication method for a semiconductor device. More particularly, the present invention relates to a structure and a fabrication method for a multiple crown capacitor in a dynamic random access memory (DRAM) cell.
2. Description of the Related Art
The capacitor is the center for signal storage in a DRAM cell. As the amount of charge being stored by the capacitor is increased, the effect of noise on the information reading, such as soft errors induced by the a particles, and the refresh frequency are greatly reduced.
Increasing the charge storage capacity of a capacitor is generally accomplished by the following methods. Substituting the dielectric layer with a high dielectric constant material increases the charge storage capacity per unit area of the capacitor. Reducing the thickness of the dielectric layer also increases the capacitance of the capacitor. The material properties of the dielectric layer and the current manufacturing technique, however, require a minimum thickness of dielectric layer. Increasing the surface area of the capacitor increases the amount of charge being stored in the capacitor; however, this also lowers the integration of a DRAM device.
The charge storage capacity for a traditional DRAM cell is normally low because a two dimensional capacitor, in another words, the planar-type capacitor, is used in the manufacturing of the integrated circuits. The planar-type capacitor occupies a great amount of the area in the semiconductor substrate designated for charge storage, and is thus not suitable for the design of a highly integrated device. A three dimensional capacitor is required for the highly integrated DRAM cell such as the stacked-type, the trench-type and the crown-type capacitor. As the memory device enters an even higher level of integration, especially in DRAM cells of 64Mb and beyond, however, a simple three dimensional capacitor structure is still not adequate. Hence, methods of increasing the surface area of a dynamic random access memory cell capacitor within a small area are being developed.